In a conventional liquid crystal display device utilizing a variable transmission polarization axis optical element for rotating a polarization axis of transmitted light, such as a TN (Twisted Nematic) liquid crystal and an STN (Super-Twisted Nematic) liquid crystal, a structure is employed in which this variable transmission polarization axis optical element is sandwiched by two sheets of polarizers.
According to such an arrangement, only a polarized light component in a specific direction is transmitted through a first polarizer located on the side of a display screen of liquid crystal, and other polarized light components are absorbed by this first polarizer. The polarization direction of light transmitted through the first polarizer is selectively changed in response to an alignment state of liquid crystal that changes with voltage applied to the liquid crystal, and the light is incident on a second polarizer located on the other side of the liquid crystal.
In the case of a liquid crystal display device of a dot matrix system, for example, in a normally white mode, regarding each pixel, (i) in a state where a voltage is not applied to the liquid crystal, the light emitted from the liquid crystal is transmitted through the second polarizer, is further reflected by a reflecting plate located at the back thereof and thereafter, is transmitted through the second polarizer, the liquid crystal, and the first polarizer again to be emitted as display light from the display screen of the liquid crystal display device; and (ii) in a state where a voltage is applied to the liquid crystal, the light emitted from the liquid crystal is absorbed by the second polarizer, and display light is not emitted from the display screen, finally.
Alternatively, in the case of a liquid crystal display device of a segment system, for example, in a region containing segment electrodes, the display light is selectively emitted from the display screen as display light in response to a state of voltage application to the liquid crystal, as in the case of the above dot matrix system. On the other hand, in a region containing no segment electrode, the liquid crystal is always in a state of non-application of a voltage, and the external light is reflected by the reflecting plate through the polarizer and the liquid crystal to be emitted as display light from the display screen.
In this way, by controlling the quantity of display light emitted from the display screen for each of the pixels or each of the segments using the liquid crystal, polarizers and so forth arranged on the optical path while reflecting the external light incident from the display screen by a reflecting film provided inside the device, reflective display is effected.
In addition, some small liquid crystal display devices of the dot matrix system, segment system or the like for use in an electronic apparatus such as a portable phone or a wristwatch arrange two sheets of color polarizers perpendicular to each other at positions opposite to the liquid crystal to effect two-color display. The color polarizers have characteristics of transmitting a specific wavelength component (color component) and of absorbing other wavelength components (color components) when transmitting a polarized light component in a predetermined direction. According to the liquid crystal display device, a region of pixel electrodes or segment electrodes in the state of voltage application is displayed in a first color, such as red, blue, green and black, and a region of pixel electrodes or segment electrodes that is not in the state of voltage application and a background other than the region are displayed in a second color, such as cyan, yellow, orange, and white.
Since, however, a polarizer which is an example of a polarized light separator effects polarization by absorbing a polarized light component in a direction different from that of a specific polarization axis in the incident light, there is a problem of poor usage efficiency of the light.
In addition, in the case of the aforementioned small display device for effecting two-color display using two sheets of color polarizers, the usage efficiency of the light is also poor, so that there is a problem of a dark display.
The present invention is made in consideration of the above problems, and an object is to provide, in a display device utilizing a variable transmission polarization axis optical element such as a liquid crystal, a display device which can effect bright two-color display during reflective display and transmissive display employing at least external light, and an electronic apparatus and a polarized light separator using the same.
The above object of the present invention is achieved by a display device including: a variable transmission polarization axis means capable of varying a transmission polarization axis; a first polarized light separating means which is arranged on one side of the variable transmission polarization axis means, which transmits light of linearly polarized light component in a first direction, and which reflects or absorbs light of linearly polarized light component in a direction different from the first direction; a second polarized light separating means which is arranged on the other side of the variable transmission polarization axis means, which transmits light of linearly polarized light component in a second direction, and which reflects, of light of linearly polarized light component in a predetermined direction different from the second direction, a component of a first wavelength .DELTA..lambda.1 and transmits a component of a wavelength -.DELTA..lambda.1 different from the first wavelength component; and a third polarized light separating means which is placed on the side opposite to the variable transmission polarization axis means with respect to the second polarized light separating means, which transmits light of linearly polarized light component in a third direction, and which reflects, of light of linearly polarized light component in a predetermined direction different from the third direction, a component of a second wavelength region .DELTA..lambda.2 and transmits a component of a wavelength region -.DELTA..lambda.2 different from the second wavelength component.
According to the display device of the present invention, when external light is incident on the variable transmission polarization axis means from the side of the first polarized light separating means, the first polarized light separating means transmits light of linearly polarized light component in the first direction in the incident external light to the side of the variable transmission polarization axis means, and reflects or absorbs linearly polarized light component in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the first direction) different from the first direction. Next, the second polarized light separating means transmits, of the light incident through the first polarized light separating means and the variable transmission polarization axis means, light of linearly polarized light component in the second direction to the side opposite to the variable transmission polarization axis means, reflects the component of the first wavelength region .DELTA..lambda.1 in the linearly polarized light components in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the second direction) different from the second direction, and transmits the component of the wavelength region -.DELTA..lambda.1 (for example, the component of the wavelength region other than the wavelength region .DELTA..lambda.1) different from the component in the first wavelength region .DELTA..lambda.1. Next, the third polarized light separating means transmits, of the light incident through the first polarized light separating means, the variable transmission polarization axis means, and the second polarized light separating means, light of linearly polarized light component in the third direction to the side opposite to the second polarized light separating means, reflects the component of the second wavelength region .DELTA..lambda.2 in the linearly polarized light components in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the third direction) different from the third direction, and transmits the component of the wavelength region -.DELTA..lambda.2 (for example, the component of the wavelength region other than the wavelength region .DELTA..lambda.2) different from the component in the second wavelength region .DELTA..lambda.2. As a result of the foregoing, either of the component of the first wavelength region .DELTA..lambda.1 reflected from the second polarized light separating means or the component of the second wavelength region .DELTA..lambda.2 reflected from the third polarized light separating means is selectively emitted from the first polarized light separating means in response to the direction of the transmission polarization axis in the variable transmission polarization axis means.
Alternatively, when external light is incident on the variable transmission polarization axis means from the side of the third polarized light separating means, the third polarized light separating means first transmits, of the incident light, light of linearly polarized light component in the third direction to the side of the second polarized light separating means, reflects the component of the second wavelength region .DELTA..lambda.2 in the linearly polarized light components in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the third direction) different from the third direction, and transmits the component of the wavelength region -.DELTA..lambda.2 (for example, the component of the wavelength region other than the wavelength region .DELTA..lambda.2) different from the second wavelength region .DELTA..lambda.2. Next, the second polarized light separating means transmits, of the light incident through the third polarized light separating means, light of linearly polarized light component in the second direction to the side of the variable transmission polarization axis means, reflects the component of the first wavelength region .DELTA..lambda.1 in the linearly polarized light components in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the second direction) different from the second direction, and transmits the component of the wavelength region -.DELTA..lambda.1 (for example, the component of the wavelength region other than the wavelength region .DELTA..lambda.1) different from the component of the first wavelength region .DELTA..lambda.1. Next, the first polarized light separating means transmits light of the linearly polarized light component in the first direction in the external light incident through the third polarized light separating means, the second polarized light separating means, and the variable transmission polarization axis means to the side opposite to the variable transmission polarization axis means, and reflects or absorbs the linearly polarized light component in a predetermined direction (for example, the direction perpendicular to or substantially perpendicular to the first direction) different from the first direction. Here, if the light transmitted through the first polarized light separating means is returned in this way by a reflecting plate or the like, the reflected light passes through the first polarized light separating means, the variable transmission polarization axis means, the second polarized light separating means, and the third polarized light separating means in the order reverse to the above order. As a result of the forgoing, either of the component of the first wavelength region -.DELTA..lambda.1 to be transmitted through the second polarized light separating means or the component of the wavelength region -.DELTA..lambda.2 to be transmitted through the third polarized light separating means is selectively emitted from the third polarized light separating means in response to the direction of the transmission polarization axis in the variable transmission polarization axis means. Incidentally, together with this emitted light, the component of the first wavelength region .DELTA..lambda.1 reflected from the second polarized light separating means and the component of the second wavelength region .DELTA..lambda.2 reflected from the third polarized light separating means are also emitted.
In this way, the second polarized light separating means effects polarized light separation by reflecting, of the incident light, the component of the first wavelength region .DELTA..lambda.1 in the linearly polarized light components different from the second linearly polarized light component. In addition, the third polarized light separating means effects polarization separation by reflecting, of the incident light, the component of the second wavelength region .DELTA..lambda.2 in the linearly polarized light components different from the third linearly polarized light component. For this reason, as compared with a conventional display device using a polarizer for effecting polarization separation by transmitting a linearly polarized light component in one direction, and absorbing a linearly polarized light component in the other direction that is perpendicular to the one linearly polarized light component, the linearly polarized light component reflected from the polarized light separating means is utilized, so that bright reflective display can be obtained.
In this case, it is possible to effect two-color display of a first color (for example, background color) composed of the component of the first wavelength region .DELTA..lambda.1 reflected from the second polarized light separating means to be emitted as display light, and a second color (for example, color of letters and numeric characters) composed of the component of the second wavelength region .DELTA..lambda.2 reflected from the third polarized light separating means to be emitted as display light. Alternatively, it is possible to effect two-color display of a first color (for example, background color) composed of the component of the wavelength region
-.DELTA..lambda.1 transmitted through the second polarized light separating means to be emitted as display light, and a second color (for example, color of letters and numeric characters) composed of the component of the wavelength region -.DELTA..lambda.2 transmitted through the third polarized light separating means to be emitted as display light. In particular, regarding the second and third polarized light separating means, it is possible to effect two-color display of desired colors by selecting the first and second wavelength regions .DELTA..lambda.1 and .DELTA..lambda.2 at the design stage.
As a result of the foregoing, the display device of the present invention allows reflective or transmissive two-color display of bright colors using external light to be effected.
According to one form of the display device of the present invention, the variable transmission polarization axis means is constructed by including liquid crystal. That is, the display device is constructed as a liquid crystal display device.
In this case, the liquid crystal may be a TN liquid crystal, an STN liquid crystal, or an ECB liquid crystal. With this arrangement, bright and high-quality two-color display can be effected with relative ease. Incidentally, this STN liquid crystal includes an STN liquid crystal using a color compensating optical anisotropic body.
According to another form of the display device of the present invention, the first polarized light separating means consists of a polarizer which transmits light of linearly polarized light component in the first direction and which absorbs light of a linearly polarized light component in the direction perpendicular to the first direction.
According to this form, the polarizer transmits the linearly polarized light component in the first direction in the incident light as linearly polarized light component in the first direction, and absorbs the linearly polarized light component in the direction perpendicular to the first direction. Therefore, two-color display can be effected on the basis of the light that is transmitted through the polarizer.
According to still another form of the display device of the present invention, the second polarized light separating means consists of a reflective polarizer which transmits light of linearly polarized light component in the second direction and which reflects light of a component of the first wavelength region .DELTA..lambda.1 in the linearly polarized light component in the direction perpendicular to the second direction.
According to this form, the reflective polarizer transmits the linearly polarized light component in the second direction in the light incident from the side of the variable transmission polarization axis means or from the side of the third polarized light separating means as the linearly polarized light component in the second direction, and reflects, of light of the linearly polarized light component in the direction perpendicular to the second direction, the component of the first wavelength region .DELTA..lambda.1 as the linearly polarized light component in the perpendicular direction, and transmits the component of the wavelength region -.DELTA..lambda.1 as the linearly polarized light component in the perpendicular direction. Therefore, when external light is incident from the side of the first polarized light separating means, the component of the first wavelength region .DELTA..lambda.1 reflected by the reflective polarizer is emitted as display light from the side of the third polarized light separating means to effect the display of the first color. Alternatively, when external light is incident from the side of the third polarized light separating means, the component of the wavelength region -.DELTA..lambda.1 transmitted by the reflective polarizer is emitted as display light from the side of the third polarized light separating means to effect display of the first color.
In this form, the reflective polarizer may consist of a laminated product in which a first layer having birefringence and a second layer having a refractive index that is substantially equal to any one of a plurality of refractive indexes of the first layer and having no birefringence are alternately laminated.
In the reflective polarizer constructed as described above, light of the linearly polarized light component in the second direction in the light incident on one main surface of the reflective polarizer from the lamination direction is transmitted as light of the linearly polarized light component of the second direction to the side of the opposite side other main surface. And, of the light of the linearly polarized light component in the direction perpendicular to the second direction, the component of the first wavelength region .DELTA..lambda.1 is reflected as light of the linearly polarized light component in the perpendicular direction, and the component of the wavelength region -.DELTA..lambda.1 is transmitted as the light of the linearly polarized light component in the perpendicular direction. In addition, light of the linearly polarized light component in the second direction in the light incident on the other main surface of the reflective polarizer from the lamination direction is transmitted as the linearly polarized light component in the second direction to the side of the opposite one main surface. And, of the light of the linearly polarized light component in the direction perpendicular to the second direction, the component of the first wavelength region .DELTA..lambda.1 is reflected as light of the linearly polarized light in the perpendicular direction, and the component of the wavelength region -.DELTA..lambda.1 is transmitted as light of the linearly polarized light in the perpendicular direction.
According to a further form of the display device of the present invention, the third polarized light separating means consists of a reflective polarizer which transmits light of linearly polarized light component in the third direction and which reflects light of a component of the second wavelength region .DELTA..lambda.2 in the linearly polarized light component in the direction perpendicular to the third direction.
According to this form, the reflective polarizer transmits the linearly polarized light component in the third direction in the light incident from the side of the second polarized light separating means or from the side opposite thereto as the linearly polarized light component in the third direction, and reflects, of the light of the linearly polarized light component in the direction perpendicular to the third direction, the component of the second wavelength region .DELTA..lambda.2 as the linearly polarized light component in the perpendicular direction, and transmits the component of the wavelength region -.DELTA..lambda.2 as the linearly polarized light component in the perpendicular direction. Therefore, when external light is incident from the side of the first polarized light separating means, the component of the second wavelength region .DELTA..lambda.2 reflected by the reflective polarizer is emitted as display light from the side of the third polarized light separating means to effect display of the second color. Alternatively, when external light is incident from the side of the third polarized light separating means, the component of the wavelength region -.DELTA..lambda.2 transmitted by the reflective polarizer is emitted as display light from the side of the third polarized light separating means to effect the display of the second color.
In this form, the reflective polarizer may consist of a laminated product in which a first layer having birefringence and a second layer having a refractive index that is substantially equal to any one of a plurality of refractive indexes of the first layer and having no birefringence are alternately laminated.
In the reflective polarizer constructed as described above, light of the linearly polarized light component in the third direction in the light incident on one main surface of the polarizer from the lamination direction is transmitted as light of the linearly polarized light component of the third direction to the side of the opposite side other main surface. And, of the light of the linearly polarized light component in the direction perpendicular to the third direction, the component of the second wavelength region .DELTA..lambda.2 is reflected as light of the linearly polarized light component in the perpendicular direction, and the component of the wavelength region -.DELTA..lambda.2 is transmitted as light of the linearly polarized light component in the perpendicular direction. In addition, light of the linearly polarized light component in the third direction in the light incident on the other main surface of the reflective polarizer from the lamination direction is transmitted as the linearly polarized light component in the third direction to the side of the opposite one main surface. And, of the light of the linearly polarized light component in the direction perpendicular to the third direction, the component of the second wavelength region .DELTA..lambda.2 is reflected as light of the linearly polarized light in the perpendicular direction, and the component of the wavelength region -.DELTA..lambda.2 is transmitted as light of the linearly polarized light in the perpendicular direction.
According to a still further form of the display device of the present invention, the angle formed by the second direction and the third direction is 45.degree. to 90.degree..
According to this form, color contrast reaches a practical level when the angle formed by the second and third directions is 45.degree., and high-purity and high-contrast two-color display can be obtained as the angle increases close to 90.degree..
In this form, the angle formed by the second direction and the third direction may preferably be 60.degree. to 90.degree..
According to this form, the color contrast is fairly improved when the angle formed by the second and third directions is 60.degree., and high-purity and high-contrast two-color display can be obtained as the angle increases close to 90.degree..
In this form, the angle formed by the second direction and the third direction may preferably be 75.degree. to 90.degree..
According to this form, the color contrast is considerably improved when the angle formed by the second and third directions is 75.degree., and high-purity and high-contrast two-color display can be obtained as the angle increases close to 90.degree..
According to another form of the display device of the present invention, a transmissive light-diffusing layer is further included between the variable transmission polarization axis means and the second polarized light separating means.
According to this form, two-color display which is not in the form of a mirror surface (in the form of a paper) can be effected by the light that is reflected from the second polarized light separating means and the third polarized light separating means, respectively, and is emitted as display light. However, the two-color display that is a mirror surface display may be effected without positively providing such a light-diffusing layer.
According to a further form of the display device of the present invention, a transmissive light-diffusing layer is further included between the second polarized light separating means and the third polarized light separating means.
According to this form, when external light is incident from the side of the first polarized light separating means, one-color display which is not in the form of the mirror surface (in the form of paper) by the light that is reflected from the second polarized light separating means and emitted as display light, and one-color display which is in the form of the mirror surface by the light reflected from the third polarized light separating means and emitted as display light can be effected in combination. Alternatively, when external light is incident from the side of the third polarized light separating means, two-color display which is not in the form of a mirror surface (in the form of a paper) can be effected by the light that is transmitted by the second polarized light separating means and the third polarized light separating means, respectively, and is emitted as display light.
According to a still further form of the display device of the present invention, a light-absorbing means is further included on the side opposite to the second polarized light separating means with respect to the third polarized light separating means.
According to this form, in particular, when external light is incident from the side of the first polarized light separating means as described above, the component of the wavelength region -.DELTA..lambda.1 and the component of the wavelength region -.DELTA..lambda.2 are absorbed by the light-absorbing means after being transmitted through the third polarized light separating means. Therefore, these components can be prevented from being emitted by being mixed to the component of the wavelength region .DELTA..lambda.1 and the component of the wavelength region .DELTA..lambda.2 that are the display light in this case, so that two-color display of vibrant colors can be effected.
According to another form of the display device of the present invention, a light source for illuminating the variable transmission polarization axis means is further included.
According to this form, on one hand, it is possible to effect the above-described two-color display mainly utilizing external light in a bright place, and on the other hand, it is possible to effect transmissive two-color display mainly utilizing a light source such as a backlight in a dark place. In the latter case, the light from the light source may be transmitted through the second and third polarization separation means so as to be emitted as display light.
According to a further form of the display device of the present invention, a reflecting means is further included on the side opposite to the variable transmission polarization axis means of the first polarized light separating means.
According to this form, in particular, when external light is incident from the side of the third polarized light separating means as described above, the component of the wavelength region -.DELTA..lambda.1 and the component of the wavelength region -.DELTA..lambda.2 are reflected by the reflecting means after being transmitted through the first polarized light separating means. Therefore, these components reflected by the reflecting means are emitted as display light from the side of the third polarized light separating means, so that two-color display of vibrant colors can be effected.
The above object of the present invention is also achieved by a polarized light separator including: one polarized light separating means which transmits light of linearly polarized component in one direction, and which reflects, of light of linearly polarized light component in a predetermined direction different from the one direction, a component of a first wavelength region .DELTA..lambda.1 and which transmits a component of a wavelength region -.DELTA..lambda.1 different from the first wavelength component; and another polarized light separating means which is located opposingly to said one polarized light separating means, which transmits light of linearly polarized light component in the other direction, which reflects, of light of linearly polarized light component in a predetermined direction different from the other direction, a component of a second wavelength region .DELTA..lambda.2 and which transmits a component of a wavelength region -.DELTA..lambda.2 different from the second wavelength component.
According to the polarized light separator, one polarized light separating means transmits, of the light incident from the opposite side of the other polarized light separating means, light of the linearly polarized light component of one direction, reflects the component of the first wavelength region .DELTA..lambda.1 in the linearly polarized light components in a predetermined direction different from the one direction, and transmits the component of the first wavelength region -.DELTA..lambda.1 different from the component of the first wavelength region .DELTA..lambda.1. In addition, the other polarized light separating means transmits, of the light incident from the side of one polarization separation means, light of the linearly polarized component in the other direction to the side opposite to the one polarized light separating means, reflects the component of the second wavelength region .DELTA..lambda.2 in the linearly polarized light component in a predetermined direction different from the other direction, and transmits the component of the wavelength region -.DELTA..lambda.2 different from the second wavelength region .DELTA..lambda.2.
In this way, if the one and the other polarized light separating means each consisting of, for example, the aforementioned reflective polarizer are employed as the second and third polarized light separating means in the aforementioned display device of the present invention, respectively, the linearly polarized light component reflected by the polarized light separator is utilized, so that bright display can be obtained. At the same time, it is possible to effect two-color display of desired colors. Incidentally, these two polarized light separating means may be combined by disposed closely, heating and pressurizing, or bonding by an adhesive. In particular, heating and pressurizing makes manufacturing easy.
The above object of the present invention is also achieved by an electronic apparatus comprising a display device as claimed in claim 1.
According to the electronic apparatus of the present invention, since the above-described display device of the present invention is included, various types of electronic apparatuses capable of effecting at least reflective or transmissive two-color display of bright colors by external light can be realized. Incidentally, the display device in any one of the above-described forms may be incorporated into the electronic apparatus of the present invention in some applications thereof.
The above object of the present invention is also achieved by a display device including: a variable transmission polarization axis optical element; a first polarized light separator which is arranged on one side of the variable transmission polarization axis optical element, and which is of a type for effecting polarization separation by reflection or absorption; a second polarized light separator which is placed on the other side of the variable transmission polarization axis optical element, and which is of a type for effecting polarization separation by reflection for every wavelength of light; and a third polarized light separator which is arranged on the side opposite to the variable transmission polarization axis optical element with respect to the second polarized light separator, and which is of a type for effecting polarization separation by reflection for every wavelength of light.
According to this display device, since the second and third polarized light separators effect polarization separation by reflection for every wavelength of light, that is, by reflecting a component of a specific wavelength in the linearly polarized light components in the direction different from the specific direction, as compared with the conventional display device using a plurality of color polarizers effecting polarization separation by absorption, the reflected linearly polarized light component is utilized, two-color display of bright colors by external light can be obtained.
Incidentally, even if the display device of the present invention as described above is constructed as the display device of any known driving system, such as a passive matrix system, an active matrix system using TFT (Thin Film Transistor) or TFD (Thin Film Diode), and a segment system, two-color display of bright colors can be realized.
In addition, as the polarized light separating means of the present invention, in addition to the above reflective polarizer, for example, means of a combination of cholesteric liquid crystal layer and (1/4).lambda. film, means for separating into reflected polarized light and transmitted polarized light utilizing Brewster angle (pages 427 to 429 of SID 92 DIGEST), means utilizing a hologram, means disclosed in the international-published international applications (International Publication Nos.: WO95/27819 and WO95/17692) may be employed. Incidentally, these various types of polarized light separators can be similarly used in place of the reflective polarizer in the embodiments to be described later.